Sunday, September 28, 2014

What a difference a week can make! Seven days ago I was in the Owens Valley and eastern Sierra Nevada, and though we got a bit of inclement weather, it was a warm storm, and we were barely inconvenienced. The pictures (here and here) show little in the way of new snow or ice. But then there was this last weekend. I was leading a short tour of Lake Tahoe for conferees at the SciX conference in Reno, Nevada, and from the moment we arrived at the lake on Friday to this afternoon, it was raining and snowing.

Fall colors and snow at Carson Pass

Lake Tahoe may have received on the order of two inches of rain, and a fair mantle of snow could be seen on the peaks above 8,000-9,000 feet. The white snow combined with the just-beginning fall colors was a beautiful sight. It kind of wreaked havoc with our field trip though. The rain was constant and the temperature never rose above 43 degrees or so. It was snowing on us at Mt. Rose Summit. Our only comfortable discussion took place inside the visitor center at Sand Harbor near Incline Village.

Lake Tahoe near Cave Rock on Saturday

Just the same, I wouldn't have changed a thing. California is in the midst of a horrific drought of epic proportions. The situation is growing desperate in California and other parts of the American Southwest and it will take several years of normal and above-normal precipitation to make up the steep deficit. An early snowfall is a good sign and hopeful beginning to the new water year.

On Highway 88 below Cook's Station

As we were coming home this evening we were treated to a wonderful sky show as the storm began breaking up. At times the cumulus clouds looked like volcanic eruptions or nuclear bombs in the distance.

Oaks and cumulus clouds near Mokelumne Hill and Valley Springs

The storm had petered out by the time we reached our prairie-lands around Milton and Oakdale. We were treated to a colorful sunset.

Friday, September 26, 2014

These things seem to happen whenever I have just left a place. I was in Mammoth Lakes only a week ago. There have been upwards of a thousand earthquakes in the last 24 hours or so. The biggest have been in the range of magnitude 3 to 3.8, which are big enough to feel. The USGS emphasizes that the quakes are tectonic (fault-related), not volcanic in origin. This is the place where fears of a volcanic eruption caused political controversy in the 1980s and 1990s (which also formed the basis for much of the movie "Dante's Peak").

We have been closely tracking an earthquake swarm in California's Long Valley
Caldera, which started yesterday at around 4AM PDT (September 25, 2014). The
swarm is located 7 miles east of the town of Mammoth Lakes, about a mile north
of the airport. From about 4 AM on the September 25th to 11AM on September 26th
there have been more than 500 earthquakes of magnitude M1.0 and above, including
8 earthquakes between M3.0 and M3.8, which were felt locally. This is one of
several earthquake swarms that have occurred in the caldera this year. Despite
the several felt earthquakes, this is still rather modest activity compared with
the much more energetic swarms occurring in the 1980s and 1990s. We do not see
any evidence for anomalous ground deformation associated with the swarm at this
time. Part of the Long Valley Caldera, known as the "resurgent dome," has been
uplifting at a rate of about an inch per year since late 2011, and this remains
unchanged. Caldera uplift has occurred sporadically for the last few decades.
The uplift rate observed since 2011 is small compared to rates observed in the
1980s and 1990s. The earthquakes themselves are small, brittle-failure (rock
breaking) events. Such events are sometimes called "tectonic." The earthquakes
do not result from the underground movement of magma. We can distinguish between
brittle-failure earthquakes and those resulting from magma movement by the
characteristics of the seismic waveforms.

I picked out some more scenes from our recent field studies class in the eastern Sierra Nevada and Owens Valley. Above, the Alabama Hills expose granitic rock essentially similar to that of the rugged high Sierra. It looks different because it weathered beneath the surface, possibly in more subtropical conditions. Cracks and fractures allow water to seep onto the surface of the granite, breaking the feldspar minerals down to clay and removing corners and edges over time.

Devil's Postpile National Monument near the headwaters of the San Joaquin River

The Devil's Postpile is a famous example of a different process of breaking up rock. When lavas flows back up and form pools, the cooling rock contracts and fractures into hexagonal shapes (although columns with 4, 5, and 7 sides are known). It is somewhat unusual to see such straight columns; they usually are far more irregular.

Mamie Lake at Mammoth Lakes

The Mammoth Lakes are a series of beautiful glacially carved tarns (some enhanced by small power generating dams). Mamie Lake is seen above, and the Twin Lakes below.

A storm blew through in the midst of our journey. The morning after brought smoke-free conditions and beautiful sunlight through the clouds. The picture below shows Mt. Tom and Mt. Humphreys west of the town of Bishop in the Owens Valley.

One of the best ways to see the Sierra Nevada is to view the range from the next ridge over. The White Mountains in any other setting would be a celebrated National Park. It is a stunning wall of rock with unique topography and unique biology. We climbed the road to the Schulman Grove of Bristlecone Pines across from the Palisades Crest of the Sierra Nevada.

Palisades Crest from the White Mountains. The Owens Valley is in the foreground.

The Palisades Crest is home to the largest remaining glaciers in the Sierra Nevada. The biggest is about a half mile long and a mile wide. In this drought year, few snow patches were left...pretty much all the ice you see in the picture above is a glacier.

The Bristlecones are special trees. Besides living in one of the toughest environments of any tree in the world (two miles in elevation, with a two or three month growing season), they grow to great antiquity. The oldest discovered thus far is more than 5,000 years in age.

The trees subsist in nutrient poor soils, but even poor soils are better than the barren debris formed on pure quartzite. The forest ends abruptly where the Cambrian quartzite begins.

The day included a spectacular view of clouds curling around the summit of Mt. Whitney (14,505 feet; 4,421 meters), the highest mountain in the lower 48 states. The spheroidally weathered boulders of granite in the Alabama Hills can be seen in the foreground.

The last day of our trip was clear, providing a beautiful view of the metamorphic rocks above Convict Lake south of Mammoth Lakes, and the tufa towers at Mono Lake. Some detailed geologic descriptions of these fascinating places are in the works for a future blog post.

Wednesday, September 24, 2014

If Geotripper has been quiet of late, there is a pretty good reason: I've been on the road and off the grid. I may have plenty to say about these scenes later on, but for now I've just gone through the entire collection and picked out the images that caught my eye for some reason or another. In the picture above, it was the one strip of sunlight on the Mono Lake tufa towers in a sky full of smoke. The lake is a vast saline evaporation pond that serves as a temporary stopover for millions of migrating birds.

Bodie Ghost Town

Bodie is a fascinating place. I picked this shot because it shows the close clustering of houses as a hedge against the barrenness of the hills beyond. I visit places like this and realize that you can choose to live comfortably in an equitable climate, or you choose to try and survive in a pitched battle with the elements. Bodie sits at 8,000 feet and suffers horrible bitter winters. It was an outpost of civilization on the edge of a hard wilderness.

Bodie Ghost Town

I still find it hard to believe that a gold mining company wanted to
turn the slope behind the town into an open pit mine just a few years ago. Some places should
remain as they are.

Owens River Gorge

Owens River Gorge is a little-known corner of the eastern Sierra Nevada that reveals some of the awesome power of earth processes. The 400 feet gorge has walls of rhyolite tuff, erupted in the space of a few hours or a few days in one of the most incredible explosions in earth history. Yellowstone's supervolcano might get all the press, but Long Valley Caldera put 150 cubic miles of hot ash into the atmosphere 760,000 years ago, blanketing the entire American West. Some deposits are found in Kansas and Nebraska. A lake formed in the caldera and eventually overflowed, allowing the Owens River to carve this deep gorge...in only a few hundred thousand years.

Lake Crowley and the Long Valley Caldera

We soon found ourselves standing on the floor of the vast Long Valley Caldera. The eruption caused the crust to collapse in a massive hole 20 miles wide and 11 miles long. The two-mile deep hole was filled with ash and lake sediments over the years, but is still a striking feature. We were standing on one edge of the vast hole, while the mountain ridge in the far distance is the other.

Mt. Tom and Pine Creek

The eastern Sierra Nevada is an astounding wall of rock that developed when the Owens Valley fault graben collapsed and sank, forming a two mile deep valley more than a hundred miles long. Mt. Tom (above) is a 13,652 feet peak rising above Round Valley near Bishop. It lies at the edge of an intrusion of granitic rock and previously existing metamorphic rock. The interaction of the hot fluids around the intrusion produced tungsten minerals that were mined for years in Pine Creek. The mine is currently mothballed.

Minaret Vista

The Minarets lie just west of the Sierra Nevada crest in the vicinity of Mammoth Lakes. The high jagged peaks reveal Triassic metamorphic rocks that developed as an ancient caldera, perhaps similar to the modern day Long Valley Caldera, collapsed into the underlying magma chamber during a giant eruption. The stunning view is from Minaret Vista on the Sierra crest just above Mammoth Ski Resort.

Monday, September 15, 2014

How strange geology is, and what wonderful journeys it provides for our imagination! So many geological processes are exceedingly slow, and yet over time incredible changes occur. How can I be talking about the edge of the continent when we are 1,000 kilometers (~600 miles) from the nearest shoreline?

I've called this narrative of our journey "Northern Convergence" because of the presence of a convergent plate boundary for the last 200 million years or so that has drastically altered and changed the continental margin of Canada and the Pacific Northwest. We had spent the previous four days traversing landscapes composed of exotic terranes, tracts of crust that originated someplace else and had been appended to the edge of the continent by way of subduction. The bits of crust were dragged into the trench, but were too buoyant to sink into the underlying mantle, so they mashed into continent instead, and intense deformation resulted. And the continent got bigger...lots bigger.

Looking downstream on the Kicking Horse River at Field, B.C.

We had crossed the Insular, Coastal, Intermontane and Omineca belts in our four days of driving, covering some 1,000 kilometers (600 miles), and we had finally reached the Canadian Rockies at Yoho National Park. It was here that we finally first encountered the ancestral edge of the North American continent. The limestone and and other sediments in the cliffs high above were deposited in a passive margin setting consisting of debris washed from the ancient continent around 900-400 million years ago. Everything west of our location was from someplace besides North America!

The scenery was on a truly grand scale. Yoho is contiguous with Banff National Park, and yet is rarely mentioned in the same breath (it's always "Banff and Jasper", maybe because they're on the Alberta side, and Alberta knows P.R.). Yet the park is spectacular, and even better, holds a treasure of worldwide significance.

The park protects mainly the upper watershed of the Kicking Horse River which includes several major icefields, including the Waputik and Wapta. The glaciers coming off the icefields contain finely ground silt and clay that stay suspended in the turbulent water. The rivers look like flowing milk at times.

Glacial "milk" also changes the appearance of lakes. In the calm water some of the clay begins to settle out forming a translucent turquoise color that is very striking. We made a stop at Emerald Lake to talk about the glaciers and have a look at the high ridge where the Burgess Shale was exposed.

Another road reaches up into the Yoho River drainage, providing access to Takakkaw Falls, the third highest in Canada at 254 meters (833 feet). The waterfall is a textbook example of a hanging valley, resulting when the main trunk glacier carved a deeper valley than the tributary glacier. The glacier feeding Takakkaw Falls is only a kilometer or so upstream of the brink.

If you need a sense of scale regarding 254 meters, look at the picture above where the water leaps outward from the cliff near the top of the waterfall. Let's zoom in on it. Those little dots to the left? Rock climbers!

All in all, Yoho National Parks is one of the most dramatic landscapes imaginable, but it's the rocks themselves that hold the real treasure. Although mining took place here last century, the treasure is in the fossils found in these rocks. About half of our crew were not with us as we toured the park, as they had left early in the morning to complete a tortuous 12 mile hike to see the quarry where the Burgess Shale fauna was discovered more than a century ago.

There is a problem with understanding the ecosystems that existed millions of years ago. Usually only the shells and bones are found, but the vast majority of organisms had soft bodies that are rarely preserved as fossils. They would invariably decay quickly. Fossil localities with the remains of soft-bodied organisms are few and precious, and our students were investigating one of the world's most famous. The Burgess Shale preserves the fossils of soft-bodied organisms that were present only a few million years after the dawn of complex multi-celled lifeforms.

How did they come to be preserved here? Just over 500 million years ago, the region was at the edge of the continent in relatively shallow water at the edge of the continental shelf. The shelf was unstable and occasionally a mass of mud would break off and sink into deeper water, carrying with it the organisms that were living there. The blocks sank into oxygen-starved water where the bacteria that would have consumed the soft body tissue could not survive. Mud covered and preserved the dead organisms. More than a hundred species have been described here.

The fossil quarry lies high on a ridge above Emerald Lake between Field and Wapta peaks. You can pick it out in the picture below, as the horizontal gash in the hillside with the lowest patch of snow. The hike is not easy, really an all-day affair. The quarry is a World Heritage Site and access is strongly restricted, and obviously collecting is not allowed. I've heard they've even gone after fossil sellers active on E-Bay.

I did the hike in 2005, so I didn't try it this time, opting instead to let my fellow professor hike with the students (she might forgive me the blisters one of these days...). The hike was one of the great adventures of my life, though, and I described it in detail in a post last April: you can read it by clicking here. There just aren't many times in life when you can be so close to the ancient past.

Holding a specimen of Marrella splendens in the Burgess Shale quarry, 2005

We visited with the local wildlife, and then headed over Kicking Horse Pass into Banff National Park. More adventures lay ahead!

A Black-billed Magpie (Pica hudsonia) at Field, B.C.

I hope that somebody appreciates that I made it through an entire post about a place named "Yoho" with nary a single "Pirates of the Caribbean" joke.

Friday, September 12, 2014

Thanks for all the attention to the post on exfoliation in Twain Harte! 4,000 hits and counting, it's been my most read blogpost in five years (about 10 or 15 times normal traffic). Today we are getting back to our tour of British Columbia and Alberta, one of the most beautiful regions in the world. We last looked at Craigellachie, the site of the completion of the Trans-Canada Railroad. As we continued down the highway, the mountains around us were becoming dramatic.

We had been traversing the Intermontane Belt, a region of high plateaus and relatively modest mountain ridges, and were now entering the Omineca Belt, a series of increasingly rugged mountain ranges, including the Purcell and Selkirk ranges, subdivisions of the Columbia Mountains. Yes, the Columbia, as in Columbia River. That's the Columbia in the picture below (actually a reservoir on the Columbia), a long distance upstream from the thread of water between Oregon and Washington in the Cascades. It is a huge watershed!

Our main goal for the day was to explore Mt. Revelstoke National Park, and the best way to do it on a tight schedule is to drive to the 1,938 meter (6,360 feet) summit. A beautiful 26 kilometer paved highway switchbacks up the flank of the mountain and ends at a parking lot just below the peak. From there one can walk a short trail to the summit area, or catch a van to the upper parking area. A network of short trails explores the alpine environment.

Storms had been wreaking gentle havoc with our trip for three days. We certainly didn't get the worst of the weather: a day before we arrived in Kamloops there had been intense thunderstorms and some areas of town were unexpectedly flooded. Drumheller, a town we would visit in a few days, was hit with a storm of golf-ball sized hailstones. Mostly we were rained on, and clouds obscured some of the views we had hoped to see (most notably at Mt. Garibaldi in the northernmost Cascades). We woke to sunshine in Kamloops, but as we drove east into the higher mountain ranges, the clouds seemed to be gathering on the higher peaks.

We reached the summit of Mount Revelstoke and had a look around. In a "cup half empty or half full" moment, the cloud deck lay just above us, so we had extensive views into the valleys below while the rugged high peaks above us were obscured. Even if partially hidden, the view was spectacular.

Mt. Revelstoke was the eighth national park in Canada, having been established in 1914. The park preserves a swath of alpine scenery from the shores of Lake Revelstoke on the Columbia River (around 500 meters, or 1,640 feet) to the summits of Revelstoke (1,938 meter, 6,360 feet) and Mt. Coursier (2,646 meters, 8,681 feet). The park encompasses four vegetation zones, an interior rain forest, subalpine Hemlock and Engelmann Spruce forest, subalpine meadows, and alpine tundra on the highest peaks. The region receives prodigious amounts of snow, and skiing was an early form of recreation on the mountain. One of the first ski jumps ever constructed was used in the park for years.

The park is not really notable for extensive rock outcrops in the most visited areas. In the very humid environment, vegetation and soils are widespread. The underlying rock is part of the Shuswap Metamorphic Complex, a series of Proterozoic and Paleozoic rocks that were deposited in the Pacific offshore of the North American Continent. The rocks were crushed into the edge of the continent in Mesozoic time, intruded here and there by Mesozoic granitic rocks, and exposed during mountain uplift in the early Cenozoic era.

The growing season on Mt. Revelstoke is exceedingly short, essentially from late June to early September, but the plants are well adapted to bloom fast and die. The park is famous for the August wildflower display, although we were a bit early to see the best of it. There were some beautiful Glacier Lilies (no good pictures, but wait for my post on Glacier National Park), and some colorful Indian Paintbrush.

As always seems the case, the clouds were starting to lift, but our time was slipping away. We enjoyed several high peaks to the north clothed in wispy clouds, but we had to start down the mountain. And of course, the sun emerged!

From midway down the mountain we had a fine view across the valley to the Monashee Mountains, home to some of the oldest rocks in British Columbia, at around 2.2 billion years. The town of Revelstoke could be seen on the narrow plain below.

Glaciers cling to the high peaks, a kind of a preview of the spectacular icefields that we would be seeing in a few days in the Canadian Rockies. We intended to visit parts of Canada's Glacier National Park, but active wildfires had closed off access to most parts of the park.

About an hour later we pulled into the small town of Golden and checked into our hotel. The storm continued to break up, giving us a beautiful sunset over the Purcell Mountains.

Tomorrow would be the beginning of the climax of our trip, an exploration of Yoho and Banff National Parks in the Canadian Rockies.

Monday, September 8, 2014

There is an ongoing geological drama going on the Sierra Nevada that may be unique (to the extent of my knowledge, which is admittedly limited in this area). Exfoliation, a process long recognized as the shaper of granitic domes and monoliths, is presently busting up the surface of a small dome at Twain Harte Lake a few miles east of the Mother Lode town of Sonora. The process has been captured on video, and is presently being monitored, due to the effects it is having on a reservoir abutment.

The event burst into the news in August when a possible dam failure warning was issued following a loud popping sound and the leakage of water from the edge of the reservoir. Once the site was investigated, a decision was reached to drain the lake until the full extent of the damage was clear. There have been at least three 'events', the last on August 3.

An employee of the lake association was very kind and allowed me to have a look at the dome and the new exfoliation shells. It was fascinating. The first thing to catch the eye was the lifeguard tower. It's tilted at an odd angle because the rock it is sitting on has been pushed upward into what is called an "A-tent" joint. My erudite and learned comment was "wow"!

Exfoliation is the breaking and fracturing of hard rocks like granite in slabs parallel to the surface of the rock. It removes corners and edges, resulting in the familiar domes found in regions like the Sierra Nevada where lots of granitic rock is exposed. It has traditionally been described as the result of 'unloading', whereby erosion strips off the overlying rock, releasing pressure and causing the rock to expand outwards, and fracturing in the process. There are some alternate explanations involving a certain amount of compression, which makes sense looking at the 'A tent' in the picture above.

There were freshly loosened slabs all over the surface of the rock, with lots of chipped edges. From the videos it is clear that the chips often snapped loose before the major slab event, like foreshocks to an earthquake (and given that earthquakes are also an example of stress release, the analogy is appropriate).

How incredible it must have been to see this happen!

The worry, of course, is the proximity of the exfoliation slabs to the abutment of the dam. A geological consulting firm is monitoring the activity, with stress meters set up in several places.

I admit I never gave it any thought, but it seems clear that the
fractures are occurring in a swarm, as the stress regime changes with
each break, placing new pressures in different sectors. Like a series of
aftershocks following an earthquake, the rocks will continue to shatter
for a period of time until a new stable regime or equilibrium is
reached. I don't know any details of how or if this process has been
witnessed in the past, so I couldn't even speculate on how long these
rock 'pops' will continue. Maybe they are already done, but I wouldn't count on it.

The picture below shows a series of fresh parallel fractures running perpendicular to the edge of the dam.

We took a closer look at the dam abutment. So far the damage is limited to the top few feet of the south margin of the dam.

In the picture below we are looking down on the edge of the dam and on the left one can see the fresh exfoliation fracture. It leads into the dam abutment.

In this next picture, we are looking closer at the edge of the dam and can see a crack running through the concrete, going down about three feet or so. The dam is around 70 years old, and had been inspected only a few months prior with no signs of problems.

No one can say that the episode is over with, but it was fascinating to see. As I said before, I'm not aware of whether this process has been monitored in real time before, and I can't find any examples of exfoliation being captured in action on film or video, although it most assuredly is happening all the time somewhere in the world. If I hear of any developments, I will pass them on.

Picture by Mrs.Geotripper

I certainly hope the good people of Twain Harte get their lake back. It looked pretty sad without any water. It is a popular swimming and fishing hole.

If you haven't seen the video, there are some very good ones on the web, courtesy of Condor Earth Technologies (click here for the link) and Dotysan, who is a local resident. Check them out!

About Me

I am a teacher of geology at Modesto Junior College and former president of the National Association of Geoscience Teachers, Far Western Section. I have led field trips all over the western United States, and a few excursions overseas, but my homebase is the Sierra Nevada, the Great Valley, and the Coast Ranges of California.

Ask Geotripper

Is there something about geology that you are curious about? Do you have questions about the scientific aspects of political controversies? I can try to provide a scientist's perspective. Your questions and possible answers could be a springboard to a blog discussion, or they can be private. Anonymity is always assumed. Contact Geotripper at hayesg (at) mjc.edu.

Blooks, Boogers and Bleries

Here are some of the series I've produced for the Geotripper Blog:

The Other California: what to see when you've seen all the really famous places in the Golden State (in progress).Into the Great Unknown: A rafting journey down the Colorado River through the Grand Canyon. The most incredible adventure of my life (so far)!

The Hawai'i That Was: An exploration of the geology, natural history, and anthropology of the most isolated lands on the planet. It's a lot more than beaches, shopping, and palm trees!